A team of paleoanthropologists have dug up the oldest human DNA yet, but rather than providing answers to our species’ origin, it has raised an array of questions and may put a lot of early human migration theories to the test.

The ancient DNA was recovered from a cave in Spain called Sima de los Huesos (the pit of bones) and dates back 400,000 years. This discovery shatters the previous record of 100,000 years.

It’s believed that the Spanish femur belonged to an enigmatic lineage of humans known as Denisovans, which are only known from 80,000-year-old remains found in Siberia, 4,000 miles east of where the new DNA was found.

“Right now, we’ve basically generated a big question mark,” said Mattihas Meyer, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “Our expectation was that it would be very early Neanderthal.”

The DNA didn’t match, though. Meyer then compared it to the samples dug up in Siberia in 2010 and was shocked to find resemblance with Denisovans.

“Everybody had a hard time believing it at first. So we generated more and more data to nail it down,” Meyer said.

The new finding is hard to reconcile with the picture of human evolution that has been emerging based on fossils and ancient DNA. Denisovans were believed to be limited to East Asia, and they were not thought to look so Neanderthal-like.

Scientists generally agree that humans’ direct ancestors shared a common ancestor with Neanderthals and Denisovans that lived about half a million years ago in Africa. This common ancestor branched out in different directions about 300,000 years ago, generating Neanderthals, Denisovans, and humans, as we know it.

To be accurate, these are all branches of human species and it’s all ready been established that the three co-existed in Asia and Europe after “humans” migrated out of Africa. It’s also been discovered that they all interbred. Later, both Denisovans and Neanderthals died out.

Meyer is hopeful that he and his team will be able to retrieve more DNA from Spanish fossils from the same site, to help solve the puzzle they have now stumbled across.

“It’s extremely hard to make sense of. We still are a bit lost here,” Meyer said.

Even though there are more questions than answers at the moment, nobody in the scientific community has raised any flags regarding whether or not evolution took place, or more accurately, is taking place.